算法 Java Leetcode Golang

Reverse a singly linked list.

Question

Reverse a singly linked list.
See it on Leetcode

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For example,
Assume that we have linked list 1 → 2 → 3 → Ø
We would like to change it to Ø ← 1 ← 2 ← 3

Hint

A linked list can be reversed either iteratively or recursively. Could you implement both?

Solution in iteratively approach

  • java
  • cpp
  • go
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/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public ListNode reverseList(ListNode head) {
    ListNode prev = null;
    ListNode curr = head;
    while (curr != null) {
        ListNode nextTemp = curr.next;
        curr.next = prev;
        prev = curr;
        curr = nextTemp;
    }
    return prev;
}

Solution in recursively approach

  • java
  • cpp
  • go
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/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode reverseList(ListNode head) {
        if (head == null || head.next == null) return head;
        ListNode p = reverseList(head.next);
        head.next.next = head;
        head.next = null;
        return p;
    }
}